Automatic steering mechanism



Jan. 2o, fss' 2,626,114

R. C. ALDERSON AUTOMATIC STEERING MECHANISM Filed May 7. 1948 3 nnen m' /7055 C 17104677.50

` portion-al mal position for higher air Patented Jan. 20, 1953 AUTOMATIC STEERING MECHANISM Ross C. Alderson, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application May '7, 1948, Serial No. 25,555

automatic steering mechanism for an aircraft as disclosed in an application of Otto Hugo Schuck and Ross C. Alderson, Serial Number 192,560 med December 13, 1947.

Iii'tlie type of steering mechanism exemplified by the aforesaid application, the displacement yof the contrfsurface which steers the craft is proto the magnitude of the deviation of 'theaircraft from a desired position. Such steerin mechanism is known as a proportional cont'rblA system. There is undesirable effect present ln 'such a proportional system. In such system thliag'nitude of control surface displacement-is the'same regardless of the speed of the craft on which theVV steering mechanism is mounted. Wheii'an 'aircraft deviates from a desired positlonftlie control surface is displaced to provide a righting moment to the aircraft, the righting fionintde'pending on' the magnitude of the deviation-and controlled thereby.

' v`.[n"'a proportional steering mechanism, as disclose'din the aforesaid application of Schuck and Alderson, the amount of control surface displacement for the same magnitude of deviation from a normal position is approximately the sameY irrespective of the air speed of the craft. A displaced control surface results in a righting moment being applied to the craft to restore it to its normal position. 'I'he righting moment resulting from a displaced control surface is a Vfunctionl of the speed of the craft and also the magnitude of'control surface displacement. rIt is desirable that the righting moment applied to the Adeviatedaircraft be approximately constant over a considerable range in air speed. In order for' the righting moment to be approximately constant it isi necessary for the control surface to be displaced a smaller amount from its norspeeds than for lower air speeds where the magnitude of deviation-is the same. A proportional systemv does not provide for this variation in control surface displacement with air speed for the same deviation.

An object therefore of my invention is to modifyy the "position of a control surface in a proportional automatic steering system in accordance with the' force on such displaced control surface.

v`Another object of my invention is to provide a novel automatic Vsteering apparatus in which the magnltude'of Vdisplacement of a control surface is ailected byffthe'force applied to such control surface.-

1o onine. (ci. '2n-'m A further object of my invention is to provide a novel automatic steering apparatus for an aircraft having a balanceable electrical circuit for controlling the actuating means for the control surface with the balance of said control circuit being affected by the force applied to the actuating means.

A further Yobject of my invention is to provide a novel automatic steering apparatus for an aircraft having a balanceable control circuit which controls the operating means for a. control surface which balance is affected by the moment applied to such control surface by the medium in which the craft moves and said apparatus includes positioning means for a trim tab associated with the control surface which is positioned in proportion to the moment applied to such control surface.

The above and further objects and novel features of the invention, as well as advantages of its arrangement, will more fully appear from the following detailed description when the same is read in connection with the accompanying draw- The drawing consists of a single gure which is a diagrammatic arrangement of my improved steering apparatus for an aircraft.

In the drawing, a main control surface II), which may be the elevator rudder or an yaileron of the aircraft, is operated by cables Il extending from a cable drum I2. The cable drum I2 is operated through means to be described by a servomotor I4. The servomotor I4 is controlled by an amplifier I5 and is electrically connected thereto for this purpose. The amplifier I5 has terminals I8. I9 which may be connected to the ship's supply or an inverter, not shown, of the aircraft. The terminals I6 and I1 of the amplifier I5 constitute the signal input terminals. The direction of rotation of servomotor Il depends upon the phase relation between the signal voltage across the terminals IB, l1 and the voltageacross terminals I8, I9. The amplifierservomotor. combination, for example, may be of the type disclosed in United States Patent 2,425,734, dated August 19, 1947, in the name of Willis H. Gille et al. A signal input circuit connected to input terminals I6, I1 of amplier I5 comprises lead 20, vertical gym-manual trim variable impedance network 2|, lead 34, rate gym-servo balance variable impedance network 3K6, lead 4.9, control surface hinge moment variableimpedance networki, lead B9, to ground and to the groundediterminal I1 of ampliflerali.

The variable impedance network2l comprises a `vertical gyro` operated potentiometer'f; a

manual trim potentiometer 23, and a transformer 24. The potentiometer 22 consists of a resistor 25 which is connected across the terminals of a secondary winding 29 of transformer 24. The transformer 24 has a primary winding 29 which may be connected to the ships supply or an inverter, not shown, of the aircraft. A wiper 26 of potentiometer 21 is adjustable over the resistor 25 and is operatively connected to a vertical flight gyro 21.

The vertical gyro 21 is of the type well known in the art having generally a rotor mounted in a casing-for rotation about a vertical spin axis and said casing is supported in a horizontal gimbal ring which in turn is pivotally mounted on a horizontal axis at right angles to the axis of support of the gyro casing in the gimbal ring. The gyro 21 is so positioned in the aircraft that upon movement of the aircraft about its pitch axis the wiper 26 moves with respect to the resistor 25.

The potentiometer 23 includes a resistor 39 which is connected across the terminals of secondary winding 28 in parallel to resistor 25, the potentiometer 23 including a Wiper 3| which is operatively connected to a manually adjustable trim knob 32. Lead 29 extends from input terminal I6 of amplifier I5 to the wiper 26 of the vertical gyro potentiometer. It is now evident that the network 2| is in the form of a Wheatstone bridge with the wipers 29 and 3| constituting the output members of the bridge. In normal position, these wipers are at the electrical centers of their respective resistors 25, and 39 so there is no potential difference between the wipers; and the bridge, consequently, has no output with the wipers as thus positioned.

Impedance network 36 consists of a rate gyro operated potentiometer 31, a servomotor opervated potentiometer 4I, a voltage divider potentiometer 45, and a transformer 44. Potentiometer 31 consists of a resistor 38 which is connected across secondary winding 48 of transformer 44. A wiper 39 of potentiometer 31 is operatively connected to a rate gyro 46.

The rate gyro 4II is of the type well known in the art having a rotor whose spin axis is mounted in a gimbal ring which ring in turn is trunnioned on an axis at right angles to the spin axis. Movement about the axis of the ring is restrained by springs or other suitable means so that the axis of the ring constitutes the axis of precession of the gyro. The magnitude of deflection about the axis of precession is a measure of the rate at which the gyro is turning about an axis perpendicular to the spin axis and the axis of precession.

Potentiometer 4I includes a resistor 42 which is connected across the ends of secondary winding 4B in parallel to resistor 38. A wiper 43 of potentiometer 4I is operatively driven through suitable operating connections 52 by the servomotor I4.

Potentiometer 45 includes a resistor 46 which has one end connected to a center tap of secondary winding 48 and has its other end connected to wiper 43 of potentiometer 4I. A slider 41 of potentiometer 45 is manually adjustable over the resistor 45.

The transformer 44 has the same primary winding 29 as transformer 24 since the several secondary windings of the various networks may have a common primary winding. A lead 34 extends from wiper 3| of the manually operable trimmer potentiometer 23 to the Wiper 39 of the rate gyro potentiometer 31.

The impedance network 50 comprises an elevator hinge moment potentiometer 53 having a resistor 54 and an adjustable wiper 55, a voltage dividing potentiometer having a resistor 65 and an adjustable tap 66, and a transformer 81 having a secondary winding 58 and a primary winding 29.

The resistor 54 is supported in insulated relation from cable drum I2 by the arms 56, 51. A lead 9| extends from one end of resistor 54 to one end of secondary Winding E9. A lead 62 extends from the opposite end of resistor 54 to the remaining end of secondary Winding 68. A lead 69 extends from wiper 55 to one end of resistor 55 of the voltage dividing potentiometer 64. A lead E3 extends from the remaining end of resistor 55 to a center tap of winding 68. The lead 69 connects the center tap of secondary Winding 68 to ground. The lead 49 connects the adjustable tap 41 of potentiometer 45 to the adjustable tap 66 of potentiometer B4.

Wiper 55 of the hinge moment potentiometer 53 is carried by an output shaft 59 of servomotor I4. The cable drum I2 which supports the resistor 54 is driven by the output shaft 59 by means of a resilient transmitting element illustrated by a spiral spring 58. One end of spring 58 is connected to the shaft 59 and the other end of spring 58 is connected by suitable means to the cable drum I2.

When servomotor I4 operates the shaft 59 and cables II to position the elevator I8 in the air stream, the air stream in turn applies a resistive moment to the elevator I0. This resistive moment on the elevator I 9 is applied through 'the elevator cables II to the drum I2. Due to presence of the resilient transmission element 58 between the servomotor shaft 59 and the drum I2, the drum may have a relative displacement with respect to shaft 59. The relative displacement of the drum and shaft depends upon the resistive moment applied to the elevator I0. Since the wiper 55 is carried by the shaft and the resistor 54 is carried by the cable drum I2, the wiper 55 and the resistor 54 will also have a relative movement depending upon the resistive moment applied by the air stream to the elevator I0. The relative displacement o-f wiper 55, with respect to resistor 54, is a measure of the resistive moment applied on the elevator I9 and is also a measure of the effort being developed by the servomotor I4.

An elevator trim tab 19 is mounted on a shaft 1I carried by the elevator IIJ. A sheave 12 is carried by the shaft 1| and from this sheave extend operating cables 13 which are operated, for example, from an inner sheave 14 of a double pulley 15, The pulley 16 is loosely carried by a shaft 84 which supports the elevator I9 for rotation in a manner well known. An outer sheave 15 of the double pulley 16 receives cables 11 which extend from a single pulley 18. The pulley 18 is driven by an output member B3 of a compensating differential 80.

The compensating differential may be of any well known type having two input arms 8| and 82 and a middle arm 83 which drives the pulley 18. The input arm 82 carries a sheave 85 which is operatively driven through cables 86 and sheave 81 from the shaft 84 which carries the elevator I8. The arm 8| is driven through a reduction gear train 98 from a trim tab motor 9|.

The motor 9| may be a capacitor type induction motor having a rotor 92 which coacts with two neld windings 93, 94. One end of winding 93 is connected to one side of line |00 and the other end of winding 93 is connected through a capacitor 95 to the other side of line |00. Line |00 may be connected to the ships supply or an inverter not shown. Winding 94 of motor 9| is connected across the output terminals 91, 90 of an amplifier 96.

Amplifier 96 includes power input terminals IOI, |02 which are connected to the line |00 and signal input terminals |03, |04. The direction of rotation of motor 9| depends upon the phase relationship between the voltage across the signal input terminals |03, |04 and the voltage across the winding 93 of motor 9|. The amplifier motor arrangement may be similar to that disclosed in a United States Patent to Taylor 2,388,350. Signal input terminal |03 is connected by means of lead |06 to the center tap of secondary winding 63. Signal input terminal |04 is connected by means of leads |05, 60 to the wiper 55 of the hinge moment potentiometer 53.

AI-Iaving described the component parts of my apparatus and the interrelationship of these parts whereby they form an automatic steering mechanism, the operation of the steering mechanism will be considered.

Operation 'I'he operation of the automatic steering mechanism is considered with respect to the departure of the control components of the steering mechanism from a datum. When the aircraft, on which the mechanism is mounted, is at the datum point or point of reckoning, the impedance network 2| is in balanced condition, that is to say. wiper 26 and wiper 3| are at the electrical centers of their respective resistors 25 and 30 with no difference of potential between them. In the impedance network 36 the wiper 39 is at the electrical center of resistor 36 and the wiper 43 is at the electrical center of resistor 42 at which time they have the same potential as the secondary winding 40 of transformer 44. In the impedance network 50 the wiper 55 is at the electrical center of resistor 54 and is at the same potential as the center tap of secondary winding 66. The elevator I and the trim tab 10 are in their normal or streamlined positions. Adjustable taps 41, 66 may be moved to approximately the mid position of resistors 45, 65 as shown.

If the aircraft is on the ground but at the attitude assumed by the aircraft at the datum point, and should it be observed that the elevator I0 is not in its normal position, it may be placed in such position by a manual adjustment. To effect this adjustment, the manual trim knob 32 is operated in one or the other directions depending upon the departure of the elevator I0 from its normal position. This operation of the trim knob 32 causes the wiper 3| to be displaced from its normal position to unbalance the network 2l; a signal is thus generated or derived between the wiper 3| and wiper 26 which is applied across the input terminals I6 and II of amplifier I5. The amplifier I causes the operation of servomotor i4 which, through the cab-les II moves the elevator I0 to its normal position. The servomotor I4 through the follow up 52 also adjusts the wiper 43 of the follow up potentiometer 4I. The wiper 43 is no longer at the potential of the center tap of secondary winding 46 so that a voltage is applied across the voltage dividing potentiometer resistor 46. The wiper 43 is positioned until the voltage between the upper end of resistor 46 of the voltage dividing potentiometer 45 and the adjustable tap 41 of the potentiometer is equal 6 and opposite to the voltage across the wipers 3| and 26 of network 2|. With the input circuit in balanced condition the servomotor I4 no longer operates.

The aircraft may now be assumed to be in flight at its normal attitude. Since the vario-us impedance networks are supplied with alternating voltage, it is assumed under the half cycle under consideration that the right end of secondary windings 28 and 4B are positive with respect to their left ends and that the upper end of secondary winding 65 is positive with respect to the lower end.

Should a transient disturbance be applied to the aircraft to cause the front of the aircraft to tilt downwardly about the pitch axis, the vertical gyro 21 in response to this downward tilt moves the wiper 26 to the right with respect to resistor 25. The rate gyro 40 also responds to the rate of movement of the aircraft about the pitch axis and also moves wiper 39 to the right with respect to the resistor 30. The input circuit to amplifier I5 is thereby unbalanced which operates and causes the servomotor I4 to rotate counterclockwise thereby to raise the elevator III. The servomotor I4, through its follow up connection 52, positions the wiper 43 toward the right end of resistor 42 to generate a voltage between wiper 43 and the secondary winding of 40 which is applied across the voltage dividing resistor 46. The voltage between the wiper 41 and the upper end of resistor 46 is in opposition to the signal derived from the vertical gyro 21 and the rate gyro 40. As the elevator I0 is being raised the air stream applies a resistive force to the elevator I0 whereby a hinge moment of the elevator about its shaft 84 is developed. This hinge moment on the elevator I0 resists the rotation of servo cable drum I2. Due to the resilient connection 58 between the cable drum I2 and the shaft 59, the shaft driven wiper 55 is displaced with respect to the resistor 54 so that the wiper is moved toward the lower end of resistor 54. The wiper 55 is now negative with respect to the center tap of secondary winding 68. The upper end of voltage dividing resistor 65 is therefore negative with respect to the center tap since it is connected by means of lead 62, wiper 55. The lower end of dividing resistor 65 is positive. therefore, with respect to the upper end. The tap 66 may be adjusted along the resistor 65 to select any desired portion of the voltage between wiper 55 and the center tap of winding 68. The servomotor I4 continues to rotate until the voltage between wiper 41 and the lower end of resistor 46 plus the voltage between tap 56 and the lower end of resistor 65 is equal but opposite to the voltage obtained from the impedance network 2| due to the movement of vertical gyro 21 and the voltage between the rate potentiometer wiper 39 and the center tap of secondary 48.

The disturbance, as stated, was transient or momentary in character. Although the hinge moment potentiometer 53 generated a signal by means of the relative displacement of wiper 55 and resistor 54 which was applied to the ampliner 96 resulting in the operation of trim tab motor 9| yet since the motor 9| operates through a reduction gear train 90 the trim tab I0 is not appreciably positioned during transient disturbances because of the high gear ratio in gearing 90.

The purpose of providing the compensating differential will now be apparent. As stated, the high ratio in gearing during transient conditions results in no appreciable movement of the input member 8I of differential 8|). It is evident that if gearing 90 directly operated the double sheave 96 and were the elevator ID moved toward the raised position as during the operation described that the sheave 'I6 would be held against rotation while the elevator Ill moved in the upward direction. This would result in a lowering of the trim tab or in a movement of the trim tab 10 toward the left from its position as shown. In order that the trim tab not be moved during this operation of the elevator, a compensating effect is provided by the differential 8f) whereby the elevator shaft 84 through the second input member 82 causes a rotation of the output member 83 which compensates for the movement of the elevator and maintains the trim tab I in its proper position with respect to the elevator IIl.

The restoring moment applied to the aircraft as the result of the upward movement of the elevator I0 causes the aircraft to move toward its normal position or the datum point. The vertical gyro 21 moves its wiper 26 toward the center of resistor 25. Since the aircraft is moving in a direction about the pitch axis opposite to that when it was subject to the transient disturbance, the rate gyro operated wiper 39 is to the left of the electrical center of resistor 38. The input circuit of amplifier I is now unbalanced. This unbalance, at this time, produces a signal voltage of opposite character than the initial character of the unbalance signal to amplifier i5. The servomotor I4 therefore rotates in an opposite direction tending to return the elevator I0 toward its normal position. The servomotor I4 rotates and drives the follow up potentiometer 43 toward the left or toward the center of resistor 42. Since the elevator is moved toward its normal position there is less force of the air stream on the elevator I0 and consequently the hinge moment signal derived from potentiometer 53 is being decreased since wiper 55 is being moved by spring 58 toward the center of resistor 54.

When the aircraft regains its original position the vertical gyro operated wiper 26 is again at datum, the rate gyro operated wiper 39 is at datum, and the follow up wiper 43 and the wiper 55 of the hinge moment potentiometer 53 are also at their normal positions. The automatic steering mechanism thus maintains or restores the aircraft to its original attitude following the action of a transient disturbing condition.

It is evident that if the transient condition were such as to cause the raising of the front end of the aircraft that the aircraft by means of the steering mechanism would also regain its original attitude by the application of down elevator rather than an up elevator as in the disturbance described.

It is evident that the voltage dividing potentiometers 45 as associated with the follow up potentiometer 4I and the hinge moment potentiometer 53 with its voltage dividing potentiometer 64 provide an arrangement whereby the elevator IIJ is positioned smaller amounts when the hinge moment, due to higher air speeds is larger than when the hinge moment due to smaller air speeds is less. It is further evident that by positioning the adjustable taps 4'I and 56 that the operation of the input circuit of amplifier I5 may vary from a pure proportional operation to one depending solely upon the hinge moment being applied to the elevator. For example, with the adjustable tap 65 moved toward the lower end, as shown, of

resistor 65 and the adjustable tap 41 moved toward the lower end, as shown, of resistor |46 the input circuit of amplifier I5 is only balanced when the servomotor I4 has positioned wiper 43 with respect to resistor 42 in accordance with any existing unbalancing signal. The actual elevator position, however, is less than the proportional displacement of servomotor shaft 59 due to the resilient driving connection 58 between the shaft 59 and the cable drum I2. The actual balance of the input circuit to amplifier I5, however, is not now affected by the hinge moment or force being applied to the elevator II) by the air stream.

If the adjustable tap 41 is moved to the upper end, as shown, of resistor 45 in the figure and the adjustable tap 66 is moved toward the upper end. as shown, of resistor 65 in the gure, then the input signal of amplier I5 is only balanced by the output of the hinge moment potentiometer 53. The output of this potentiometer depends upon the righting moment being applied to the aircraft by the elevator or to the hinge moment being applied to the elevator. The moment on elevator III varies with the speed of the aircraft as well as the displacement of the craft from datum. The righting moment provided by the displaced elevator is thus maintained constant as less elevator displacement is incurred for the same departure from datum as the air speed increases. That is to say, the balancing signal provided by the hinge moment potentiometer 53 is the same when the hinge moment is constant and this potentiometer thus controls the servomotor I4 through the network of amplifier I5 to decrease the amount of displacement of elevator IIl as the air speed increases.

With the taps 41 and SI5- at the upper end of resistor 45, and 65, as stated, the apparatus will maintain the attitude of the craft as desired despite the presence of a continuous disturbance. The operation of the steering mechanism will thus be considered when a continuous rather than a transient disturbing moment is being applied to the aircraft. This disturbing moment may, for example, be the result of a change in the position of the center of gravity along the longitudinal axis of the aircraft. If the center of gravity moves toward the front of the aircraft, the front of the aircraft will move downwardly about the pitch axis. The vertical gyro and the rate gyro will move their respective wipers toward the right as in the case of the transient disturbance described whereby the input circuit of amplifier I5 is unbalanced causing the operation of servomotor I4 to move the elevator I0 in an upward direction. This movement of the elevator by the servomotor is followed by the movement of the rebalancing potentiometer wiper 43 which now has no effect on the signal circuit and the movement of wiper 55 of the hinge moment potentiometer with respect to resistor 54 which latter potentiometer balances the amplifier input circuit. Under the righting moment of the applied elevator the aircraft moves toward its original position. The wiper 26, controlled by the vertical gyro 21, for purpose of analysis, does not immedialtely return to its center position on resistor 25 since the mechanism must provide a partial displacement of the elevator to counteract the continuous disturbing moment being applied to the aircraft. In other words, the attitude of the aircraft has altered to provide a sufficient displacement of the elevator I 0 to compensate for the continuous disturbing moment being applied to the aircraft.

The wiper 55 of the hinge moment potentiometer 53 is displaced toward the lower end of resistor 54 as shown. due to the compensating position of the elevator l0. This continuous displacement of wiper 55 with respect to resistor 5t causes a signal to be applied to the amplifier BB which causes the trim tab motor 9| to operate through the gearing 9|) and differential 8l), sheave 18, double pulley 15, and cable 13 to position the trim tab 'I0 in a downward direction. The positioning of the trim tab 'Ill downwardly results in an upward moment being applied to it from the air stream, which moment tends tooppose theY downward moment being applied to the elevator Hl by the air stream. The force on the main eley vator cables Il thereby decreases and the'resilient connection 58, moves the resistor 54 counterclockwise toward its normal position with respect to wiper 55. The hinge moment potentiometer 53 therefore generates a smaller signal which results in the unbalancing of the input circuit to ampliiler l5. The amplifier I causes the servomotor I4 to rotate further in a counterclockwise direction thereby moving the elevator l0 to a greater upward angular displacement.

The operation of the mechanism is continuous. The increased angular displacement of the elevator I0 results in a balancing signal being provided by the hinge moment potentiometer 53 to the input circuit of amplifier l5. This signal from the potentiometer 53 also in turn causes further operation of the slowly moving operating meansl for the trim tab which decreases the hinge moment potentiometer signal. The further positioning of the elevator Hl results in restoring the aircraft to its normal attitude. At this time the wiper 26 is at the electrical center of resistor 25 and the wiper 55 of the hinge moment potentiometer 53 is at the electrical center of resistor 54. The moment being applied to the elevator Hl is counterbalanced by the moment in an opposite direction derived from the trim tab 10. The normal attitude is maintained by the craft despite the continuous disturbing moment.

Itis now evident that I have provided an automatic steering mechanism for an aircraft which includes novel means for governing the extent of control surface displacement in accordance with the reactive force or reactive moment of the air stream on such displaced control surface so that the control surface displacement is modiiied with air speed. In this novel steering mechanism, I have also provided for the automatic trim of an aircraft by associating with the means responsive to the reactive moment of the air stream on a displaced control surface an automatic trim tab positioning device for positioning the trim tab to compensate for the reactive moment on the control surface.

Although but one embodiment of the invention has been illustrated and described, various changes and modifications in the form and relative arrangement of the components of the embodiment, which will now appear to those skilled in the art. may be made without departing from the scope of the invention. Reference may be made to the appended claims for a deiinition of the limits of the invention.

I claim as my invention:

l. Control apparatus for an aircraft having a control surface, said apparatus comprising: a vertical gyro; means for generating a first signal upon tilt oi' said gyro about one axis; control surface power means; follow-up means operated by said power means for generating a second signal; means responsive to the force developed by said power means in positioning said control surface for generating a third signal; means for combining said signals; and means controlled by said combining means for operating said power means.

2. Control apparatus for an aircraft having a control surface, said apparatus comprising: means responsive to a condition for deriving a rst signal proportional to the magnitude of said condition; control surface power means for deriving a second signal proportional to the magnitude of movement of said power means; means for selecting a portion of said second signal; means for deriving a third signal proportional to the reactive force of said control surface on said power means; and combining means controlled by the rst, third and the selected portion of said second signal and adapted to control said power means whereby selecting various portions of said second signal modifies the extent of control surface movement.

3. Control apparatus for an aircraft having a. control surface provided with a trim tab comprising: attitude responsive means; means for deriving a signal in proportion to the magnitude of movement of the attitude means about an axis; control surface power means; means for deriving a signal proportional to theV reactive force between said control surface and said power means; means for combining said attitude signal and said power means signal and operatively controlling said power means; trim tab power means; operating means for said trim tab power means; and means for connecting said operating means to said power means signal deriving means, whereby positioning of said trim tab removes said reactive force and permits said attitude means to restore the craft to original position.

4. Control apparatus for an aircraft having a control surface provided with a trim tab, said apparatus comprising: control surface power means; trim tab motor means; craft position responsive means; control means for said power means and operated by said responsive means; follow-up means driven by said power means, means responsive to the effort developed by said power means, said follow-up and said eiIort responsive means operating said control means in opposition to said craft position means; and means for controlling said trim tab motor means and also operated by said effort responsive means.

5. Control apparatus for an aircraft having a control surface, said apparatus comprising: position responsive means; control surface power means; control means for said power means; means for generating an electrical signal in proportion to the movement of said responsive means from a predetermined position and operating said control means; means responsive to the effort developed by said power means for generating an electrical signal for said control means in opposition to said signal from said position responsive means; and automatic trim means also responsive to said effort signal for removing the load on the power means and thereby reducing said effort signal to thereby cause further operation of said control means from said position responsive signal means.

6. Control apparatus for an aircraft having a control surface, said apparatus comprising: position responsive means; power means; control surface operating means driven by said power means; control means for operating said power means; means operated by said responsive means for generating a signal to effect operation of said control means; means responsive to the effort applied to said operating means for generating a signal for said control means in opposition to said position responsive means signal; a trim tab power means having a slow response; and means for controlling said trim tab power means from the operating means signal generating means to reduce the magnitude of said signal from said operating means.

'7. Control apparatus for an aircraft having a control surface, said apparatus comprising: a power means; means on said aircraft for deriv ing a rst signal in proportion to change of position of said aircraft to effect operation of said power means; means for operating said control surface and driven by said power means; means actuated by said operating means to derive a second signal in proportion to the effort applied to said operating means to oppose said first signal; and means also responsive to said second signal for reducing the eiort applied to said operating means to thereby modify said second signal.

8. Control apparatus for an aircraft having motor means for changing the attitude of said craft, said apparatus comprising: control means for reversibly operating said motor means; a balanceable network connected to said control means and causing operation thereof upon unbalance of said network, said network including three signal generators for affecting said balance; means for operating one of said generators to effect operation of said motor means; follow-up means driven by said motor means in proportion to its extent of movement for operating a second signal generator; and means operated in proportion to the force opposing said motor means for adjusting a third signal generator, whereby when no opposing force is applied to said motor said network is rebalanced by said follow-up means.

9. Control apparatus for an aircraft having motor means for operating a control surface for changing the attitude of said craft. said apparatus comprising: control means for reversibly operating said motor means; a balanceable network connected to said control means and causing operation thereof upon unbalance of said network, said network including a plurality of signal generators for affecting said balance; means for operating one generator to eifect operation of said motor means; follow-up means driven by said motor means in proportion to its extent of movement for operating a second signal generator; and means operated in proportion to the force opposing said motor means for adjusting a third signal generator, means for varying the signal from said third generator applied to said network whereby movement of said control surface proportional to the operation of said iirst signal generator is obtained.

10. Control apparatus for an aircraft having motor operated means for changing the position of said craft about an axis, said apparatus comprising: control means for reversibly operating said motor; a rst signal means for initiating operation of said control means; a second signal means operated in proportion to the extent of movement of said motor; a third signal means operated in proportion to the force opposing operation of said motor; signal combining means connected to said signal means and electrically connected to said control means; and means for opposing the effect of said first signal on said control means by either said second or said third signals.

ROSS C. ALDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,183,932 Carlson Dec. 19, 1939 2,232,982 Tank Feb. 25, 1941 2,451,263 Webb Oct. 12, 1948 2,475,484 DeNise July 5, 1949 2,511,846 Halpert June 20, 1950 2,568,719 Curry, Jr Sept. 25, 1951 

